Magnetically guided catheters

ABSTRACT

A magnetically-guided catheter includes a tip positioning magnet in the distal electrode assembly configured to interact with externally applied magnetic fields for magnetically-guided movement. A magnetically-guided mapping catheter includes an electrically-conductive capsule in the form of a casing that includes a distal ablation surface and isolates the positioning magnet from bio-fluids to prevent corrosion. An open irrigation ablation catheter includes an isolated manifold that isolates the positioning magnet from contact with irrigation fluid to prevent corrosion.

BACKGROUND OF THE INVENTION

a. Field of the Invention

The present invention relates generally to medical instruments, and morespecifically, to catheters navigable within the body of a patient usingexternally applied magnetic fields.

b. Background Art

Electrophysiology (EP) catheters have been used for an ever-growingnumber of procedures. For example, catheters have been used fordiagnostic, therapeutic, mapping and ablative procedures, to name just afew examples. Typically, a catheter is manipulated through the patient'svasculature to the intended site, for example, a site within thepatient's heart, and carries one or more electrodes, which may be usedfor mapping, ablation, diagnosis, or other treatments. Precisepositioning of the catheters within the body of the patient is desirablefor successful completion of the above procedures. In general, suchcatheters may be complex in their construction and therefore difficult(and expensive) to manufacture.

To position a catheter within the body at a desired site, some type ofnavigation must be used, such as using mechanical steering featuresincorporated into the catheter (or an introducer sheath). Anotherapproach has been developed, namely, providing magnetically guidedcatheter devices that are navigated through the patient's body usingexternally-generated magnetic fields. More specifically, magneticstereotactic systems have been developed that are particularlyadvantageous for positioning of catheters, as well as other devices,into areas of the body. The externally-generated magnetic fields andgradients are generated to precisely control the position of thecatheter within the patient's body. Such stereotactic systems operate bymonitoring the position of the catheter tip in response to the appliedmagnetic fields and, using well established feedback and controlalgorithms, controlling the fields so that the catheter tip is guided toand positioned in a desired location within the patient's body. Oncepositioned, physicians may operate the catheter, for example, to ablatetissue to interrupt potentially pathogenic heart rhythms or to clear apassage in the body.

However, the magnetic response of the catheter in such magnetic guidancesystems can be a limitation on the precise control of a catheter.Improvements in catheters utilized with magnetic guidance and controlsystems, such as stereotactic systems, are desired. Specifically, a lowcost, yet high performance magnetically guided catheter is desirable.

As further background, it is known generally that catheter ablation(e.g., RF ablation) may generate significant heat, which if notcontrolled can result in undesired or excessive tissue damage, such assteam pop, tissue charring, and the like. It is therefore common (anddesirable) to include a mechanism to irrigate the target area and thedevice with biocompatible fluids, such as a saline solution. The use ofirrigated ablation catheters can also prevent the formation of softthrombus and/or blood coagulation. There are two general classes ofirrigated electrode catheters, i.e., open irrigation catheters andclosed irrigation catheters. Closed ablation catheters usually circulatea cooling fluid within the inner cavity of the electrode. Open ablationcatheters typically deliver the cooling fluid through open outlets oropenings on or about an outer surface of the electrode. Open ablationcatheters often use the inner cavity of the electrode, or distal member,as a manifold to distribute saline solution, or other irrigation fluids,to one or more passageways that lead to openings/outlets provided on thesurface of the electrode. The saline thus flows directly through theoutlets of the passageways onto or about the distal electrode member.

One challenge in developing a magnetically-guided, open-irrigatedablation catheter, however, is how to deploy a tip positioning magnet soas to avoid contact with the irrigation fluid. This challenge stems fromthe fact that the magnetic material that would typically be used in thetip positioning magnet is highly susceptible to corrosion when exposedto irrigation fluid. It would therefore be desirable to provide amagnetically-guided catheter design that reduces or minimizes materialcorrosion.

There is therefore a need to minimize or eliminate one or more of theproblems set forth above.

BRIEF SUMMARY OF THE INVENTION

One advantage of the methods and apparatus described, depicted andclaimed herein, in embodiments suitable for use in magnetically-guidedirrigated ablation catheters, involves configurations that preventirrigation fluid (e.g., saline) from coming into contact with apositioning magnet, thus preventing corrosion while retaining all thefeatures of an irrigated magnetic electrode for RF ablation. Anotheradvantage, in embodiments suitable for use magnetically-guided electrodecatheters, involves configurations that prevent bio-fluids from cominginto contact with the positioning magnet, thus preventing corrosion.

An electrode assembly embodiment suitable for use in amagnetically-guided open-irrigation ablation catheter includes an body,a manifold and an outer capsule. The body has a proximal shank portionand a distal (enlarged) portion and includes a tip-positioning magnet.The manifold includes a distribution cavity configured to receiveirrigation fluid and an irrigation passageway in fluid communicationwith the distribution cavity which has a distal exit port for deliveryof irrigation fluid. The manifold is configured to isolate the body(i.e., the magnetic material) from the cavity and passageway, thus alsoisolating the body from contact with irrigation fluid. The outer capsulesurrounds the magnetic body and comprises electrically conductivematerial, which may be selectively energized. When energized, the distalportion of the outer capsule acts as an ablation surface.

In an embodiment, the body may comprise conventional magnetic materials(e.g., ferromagnetic), rare-earth compositions (e.g., Neodymium IronBoron—NdFeB) or an electro-magnet. In another embodiment, the manifoldmay comprise a self-supporting tubular structure that is containedwithin the body. In a further embodiment, the manifold may comprise anisolation coating applied to the body. Since the body contains certainfeatures, such as longitudinally-extending grooves, these same featuresremain after being coated. The outside surfaces of the coated featurescooperate with the inside surfaces of the outer capsule to create themanifold. In a still further embodiment, the outer capsule comprises anelectrically-conductive coating, which may include multiple layers. Thecoating isolates the body from external bio-fluids that may causecorrosion. In yet another embodiment, the outer capsule comprises anelectrically-conductive casing, which may include a tip cap, shank coverand a washer configured to cooperatively seal together and comprisingelectrically-conductive material, such as platinum or platinum alloys.

In a still further embodiment, an electrode assembly is provided that issuitable for use in a magnetically-guided electrode catheter (e.g.,mapping catheter). The assembly includes an body and an outer casing.The body has a proximal shank portion and a distal relatively enlargedportion wherein the body includes a tip-positioning magnet. The outercasing surrounds the body. The outer casing includes a cup-shaped tipcap configured to cover the distal portion of the body and acylindrical-shaped shank cover configured to encase the shank portion ofthe body. The casing comprises electrically conductive material so as toallow electrical interaction with an external device (e.g., mappingapparatus). The electrode assembly, particularly the shank cover, isconfigured to receive the distal end portion of a catheter shaft.Methods of manufacture are also presented.

The foregoing and other aspects, features, details, utilities, andadvantages of the present disclosure will be apparent from reading thefollowing description and claims, and from reviewing the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a first electrode assembly embodiment asused in a magnetically-guided catheter.

FIG. 2 is an enlarged side view of the distal tip assembly of thecatheter of FIG. 1, having a tip electrode assembly and a ring electrodeassembly.

FIG. 3 is an isometric view of a positioning magnet (i.e., body)incorporated into the tip electrode assembly of FIG. 2.

FIGS. 4-5 are isometric views showing an intermediate stage ofmanufacture where a tip cap, ring and shank cover are assembled over andonto the tip positioning magnet of FIG. 3.

FIG. 6 is a side view of the tip electrode assembly of FIG. 2.

FIG. 7 is a cross-sectional view of the tip electrode assembly of FIG.2.

FIG. 8 is an isometric view of the tip electrode assembly of FIG. 2showing an electrical connection and a safety line.

FIG. 9 is an enlarged isometric view of the encircled region of FIG. 8.

FIG. 10 is cross-sectional view of the tip electrode assembly of FIG. 2including connections.

FIG. 11 is an isometric view of a second electrode assembly embodimentsuitable for use in a magnetically-guided, irrigated ablation catheter.

FIG. 12 is cross-sectional view of the electrode assembly of FIG. 11.

FIG. 13 is an exploded, isometric view of the electrode assembly of FIG.11, showing an electrode base, an isolated manifold and an electrodetip.

FIG. 14 is an isometric view of the electrode tip of FIG. 13 taken froma proximal point of view.

FIG. 15 is an isometric view showing a sub-assembly of the electrodeassembly of FIG. 11 in a first stage of manufacture.

FIG. 16 is an isometric view showing a sub-assembly of the electrodeassembly of FIG. 11 in a second stage of manufacture.

FIG. 17 is an exaggerated cross-sectional view of anelectrically-conductive coating suitable for encapsulating thesub-assembly of FIG. 16.

FIG. 18 is an isometric view of the electrode assembly of FIG. 16showing the un-trimmed tail ends of a plurality of irrigation tubes.

FIG. 19 is an isometric view of a third electrode assembly embodiment,shown partially in cross-section, suitable for use in a magneticallyguided, irrigated ablation catheter.

FIG. 20 is a partial cross-sectional view of the proximal end portion ofthe electrode assembly of FIG. 19, showing irrigation fluid flow pathsisolated from the magnetic body.

FIG. 21 is an isometric view of a sub-assembly of FIG. 19 in a firststage of manufacture.

FIG. 22 is an isometric view of the sub-assembly of FIG. 19, shownpartially in cross-section.

FIG. 23 is an isometric view of a sub-assembly of FIG. 19 in a secondstage of manufacture.

FIG. 24 is an isometric view of the fully manufactured tip electrodeassembly.

FIGS. 25A-B are side views of respective machining approaches forproducing magnet pellets.

FIG. 26 is a side view of a fourth electrode assembly embodimentsuitable for use in a magnetically guided, irrigated ablation catheter,having a multi-segment tip positioning magnet.

FIG. 27 is an end view of the multi-segment magnet of FIG. 26.

FIG. 28 is an enlarged view of the multi-segment magnet of FIG. 27.

FIG. 29 is a sleeve used in a method of manufacturing the multi-segmentmagnet of FIGS. 26-28.

FIG. 30 is a chart showing magnetic field strength of a multi-segmenttip positioning magnet.

FIG. 31 is a diagrammatic view of a segment of a multi-segment magnetshowing different regions of magnetization.

FIG. 32 is an end view of multi-segment magnet having alternatingmagnetic orientations for adjacent segments.

FIG. 33 is simplified cross-section view of a lumen clearing embodimentusing an alternating pole multi-segment magnet.

FIG. 34 is a block and diagrammatic view of a robotic catheter systemhaving a distal rotatable portion employing an alternating polemulti-segment magnet.

FIGS. 35A-35B are simplified isometric views of the distal rotatableportion of the catheter of FIG. 34, which includes a functional featureblock, in first and second rotary positions, respectively.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings wherein like reference numerals are usedto identify identical components in the various views, FIGS. 1-10 showvarious aspects of a first electrode assembly embodiment. FIG. 1 inparticular is a simplified, isometric view of a single-use magneticallyguided catheter 100 that includes such an electrode assembly 112 at thedistal end portion and operatively adapted for conducting a diagnosticor a therapeutic procedure under clinician control. In the illustratedembodiment, catheter 100 is a non-irrigated mapping catheter. Catheter100 generally includes a flexible shaft in the form of an outer tube 102having a proximal end portion 104, a distal end portion 106 andparticularly including a relatively flexible segment 108. The softsegment 108 is configured so as to facilitate navigation of the catheterthrough the use of externally-applied magnetic fields interacting with atip positioning magnet, as described in greater detail below. Of course,the segment 108 can be fabricated with a variety of different degrees offlexibility (e.g., analogous to a fishing pole having a graduated andincreasing degree of flexibility from proximal to distal portions).Catheter 100 further includes an electrical connector 110 configured toestablish electrical connection(s) between electrode portions of acatheter tip assembly 112 and external electrical apparatus (not shown)to perform, for example, mapping, ablation and/or pacing procedures, orto perform other aspects of a medical procedure. FIG. 1 further shows anintroducer 114, in connection with which catheter 100 may be used.

Before proceeding to the detailed description, a brief overview of thecontemplated use of the disclosed embodiments will first be set forth.The electrode assembly contained in catheter 100 (as well as the otherelectrode assembly embodiments described herein) is of the type thatincludes at least one positioning magnet in the tip assembly 112. Thetip positioning magnet is configured to cooperate withexternally-generated magnetic fields to provide for the guidance (i.e.,movement) of the catheter tip to a desired location within the body.Thus, in operation, catheter 100, specifically tip assembly 112, may benavigated to a site in the body to perform a medical procedure, such asan atrial mapping, pacing and/or ablation. For example only, distal tipassembly 112 may extend into a heart chamber of a patient. Once thedistal tip assembly 112 is disposed within the heart chamber, a magneticfield is applied which interacts with the tip positioning magnet,particularly the magnetic field produced by the tip magnet, to exert anorienting force on the tip assembly, allowing for precise positioning ofthe catheter tip assembly. The externally-generated magnetic fields usedto orient the tip assembly 112 may be, in one embodiment, generatedusing a magnetic stereotactic system (not shown). Such stereotacticsystems are known in the art and are commercially available from, forexample only, Stereotaxis, Inc. of St. Louis, Mo. and Maple Grove, Minn.Such systems may include movable source magnets outside the body of thepatient, and operative details of such systems are disclosed in, forexample, U.S. Pat. Nos. 6,475,223 and 6,755,816, the disclosures ofwhich are hereby incorporated by reference in their entirety. Whilecatheter 100, as well as catheters employing other electrode assemblyembodiments disclosed herein, may be advantageously used with astereotactic system, the invention contemplates that magnetic fields andgradients to deflect the catheter tip assembly 112 may be alternativelygenerated by other systems and techniques.

With continued reference to FIG. 1, flexible tubing 102 may befabricated according to known processes, such as multilayer processingincluding extrusion processes, mandrel-based processes and combinationsthereof from any suitable tubing material known in the art of medicalinstruments, such as engineered nylon resins and plastics, including butnot limited an elastomer commercially available under the tradedesignation PEBAX® from Arkema, Inc. of a suitable durometer, meltingtemperature and/or other characteristics. In this regard, in oneembodiment, the soft segment 108 comprises material that providesgreater flexibility than the proximal remainder portion of shaft 102.For example only, shaft 102 other than in soft segment 108 may comprisematerial having a 72D (durometer) hardness and include braided materialfor kink reduction. The soft segment 108 may be non-braided material andhave a 25D, 35D or 40D hardness (i.e., more flexible). The soft segment108 is configured to allow for improved magnetic guidance through thecontrol of externally-applied magnetic fields, as described above. Inother words, the soft segment 108 allows precise positioning of the tipwithout having to overcome stiffness in the shaft. In a furtherembodiment, shaft 102 may be about 52.525 inches (128 cm) in length withthe soft segment being about 5.375 inches (13.7 cm) in length. In astill further embodiment, shaft 102 may be 5F (French) in size with a 7Fflare at the distal end portion 106, which is configured for a press-fitconnection with tip assembly 112. Of course, variations are possible.

Electrical connector 110 may comprise a known connector configured toengage the external electronics (not shown) with, for example, a plug-inconnection. One suitable electrical connector is a 14 pin REDEL® plasticconnector commercially available from LEMO of Rohnert Park, Calif.,although other connectors from various manufacturers may likewise beutilized. Although not shown, such external electronics may comprise, inthe case of a mapping catheter such as catheter 100, visualization,mapping and navigation components known in the art, including amongothers, for example, an EnSite Velocity™ system running a version ofNavX™ software commercially available from St. Jude Medical, Inc., ofSt. Paul, Minn. and as also seen generally by reference to U.S. Pat. No.7,263,397 entitled “METHOD AND APPARATUS FOR CATHETER NAVIGATION ANDLOCATION AND MAPPING IN THE HEART” to Hauck et al., owned by the commonassignee of the present invention, and hereby incorporated by referencein its entirety. Additionally, an electrophysiological (EP) monitor ordisplay such as an electrogram signal display or other systemsconventional in the art may also be coupled (directly or indirectly).

FIG. 2 is an enlarged, side view showing, in greater detail, tipassembly 112. The tip assembly 112 includes a tip electrode assembly116, a ring electrode assembly 118 and a plurality of electricalconductors 120. The tip electrode assembly 116 includes a proximalpassive portion 122 and a distal active portion 124. The outsidediameter (OD) of the proximal passive portion 122 is configured for apress-fit coupling with the inside diameter (ID) of shaft wall 126.Accordingly, the proximal passive portion 122, after connection to shaft102, does not present an electrically conductive surface, for example,for mapping, localization and the like. Conversely, the distal activeportion 124 remains exposed even as incorporated into catheter 100, andis thus configured to present an electrically conductive surface, forexample, for electrical interaction with tissue. In one embodiment,active portion 124 comprises for example a 7F (i.e., diameter), 4 mm(i.e., length) exposed tip, although variations are possible as one ofordinary skill in the art will appreciate.

The ring electrode assembly 118 includes a plurality of ring electrodes128 _(R-2), 128 _(R-3) and 128 _(R-4). Like the distal active portion124, the ring electrodes 128 _(R-2), 128 _(R-3) and 128 _(R-4) remainexposed even as incorporated into catheter 100 and thus present anelectrically conductive surface, for example, for mapping, localizationand the like. In one embodiment, inter-electrode spacing may be equaland may be approximately 2 mm. The tip electrode, active portion 124 andring electrodes 128 _(R-2), 128 _(R-3) and 128 _(R-4) are electricallycoupled to electrical connector 110 by way of electrical conductors 120.

FIG. 3 is an isometric view of a magnet body 130 (also referred toherein as the tip positioning magnet) of tip electrode assembly 112. Thebody 130 is generally the innermost component of tip electrode assembly116. The body 130 is generally cylindrical in shape, extending along anaxis “A” and includes a proximal shank portion 132 having a firstdiameter 134 and a distal tip portion 136 having a second, largerdiameter 138. Distal tip portion 136, while generally cylindrical,includes a generally hemispherical distal surface 140. The body 130further includes a shoulder 142 at the transition between shank portion132 and distal tip portion 134 and may further include a blind bore 144(best shown in FIG. 7 as denoted by reference numeral 168 therein). Inone embodiment, the body 130, after final magnetization (describedbelow), produces a magnetic field oriented along axis A, having a north(N) pole (i.e., from which magnetic field lines extend) at the distalend portion and a south (S) pole (i.e., to which magnetic field linesterminate) at the proximal end portion.

In an embodiment, body 130 may be a permanent magnet fabricated from aknown magnetic materials, such as ferromagnetic materials, or inalternative embodiments, fabricated from compositions includingrare-earth materials, such as neodymium-iron boron-43 (NdFeB-43),neodymium-iron boron-45 (NdFeB-45), neodymium-iron boron-48 (NdFeB-48)or neodymium-iron boron-50 (NdFeB-50). Other magnet materialcompositions may be used; however, it should be appreciated that anyparticular selection of an alternate magnetic material composition willinvolve balancing of the resultant magnetic field strength of the tippositioning magnet versus the externally-generated magnet field strengthdeveloped by the external magnetic guidance systems (i.e., the resultingforce developed on the catheter tip for guidance is a function of bothmagnetic field strength levels).

In an embodiment, body 130 is manufactured in a multi-step powderedmetallurgical manufacturing process. First, the magnetic material (e.g.,micron size Neodymium and iron boron powder) are produced in an inertgas atmosphere. Second, the magnetic material is pressed or compacted(i.e., compressed) in a mold, for example, in a brick or block shape andthen the material is heated in a sintering step to render the materialas a unitary structure. The result is a brick or block shaped slug. Themagnetic performance may be optimized by applying a magnetic fieldeither before, after, or during compaction (and/or sintering) whereinthe applied field imparts a desired direction of magnetization ororientation in the NdFeB alloy magnet. The sintered slug may then besub-divided into pieces. The individual pieces may thereafter bemachined into their final form having the desired shape and dimensionsusing conventional approaches (e.g., diamond tooling for grinding,electrostatic discharge machining (EDM) or the like). Note, thismachining step is preferably performed when the pieces are in anun-magnetized state.

FIGS. 25A-B are simplified side views of multiple approaches formachining the sintered pieces. FIG. 25A shows a first embodiment thatinvolves a fixture 127 a configured with a cutting surface 129 a (e.g.,diamond tipped). The cutting surface 129 a may correspond to the wholelength of the machined piece 130 a. The workpiece 130 a is rotated aboutaxis A, while relative movement is imparted between the fixture 127 aand the workpiece 130 a in a direction substantially normal to axis A soas to cut the workpiece 130 a in the shape of (i.e., the profile of) thecutting surface 129 a. In one embodiment, the fixture 127 a is movedtoward the workpiece in the direction 131 a to commence machining andthen moved away from the workpiece, also in direction 131 a, when thecutting/machining operation has been completed. Of course, in thealternative, the workpiece 130 a may be moved relative to the fixture127 a, or some combination of movements by each of the fixture andworkpiece are possible.

FIG. 25B shows a second embodiment for machining a workpiece 130 b thatinvolves a cutting tip 127 b having a cutting surface 129 b configuredfor movement along a toolpath 131 b. The cutting tip 127 b may be adiamond-tipped cutting bit or the like and may be coupled to movementmechanism 133. In an embodiment, the mechanism 133 may be configured toboth move (i.e., rotate) workpiece 130 b about axis A as well as move(i.e., linear movement) the cutting tip 127 b along the toolpath 131 b(e.g., the mechanism 133 may be a lathe having a moveable tip positionrelative to axis A). In a further embodiment, the mechanism 133 may be aCNC lathe where the toolpath 131 b may stored in a memory as datacorresponding to the toolpath 131 b. One advantage of the method ofmanufacture using the arrangement of FIG. 25B is the reduced cost of thecutting bit 127 b, for example, as compared to the whole-length customfixture 127 a shown in FIG. 25A, with a custom configured surface 129 b.

Finally, the machined pieces (“pellets”) are subjected to a magneticfield sufficient to magnetize the pellets to saturation. In a stillfurther embodiment, in the step above where the sintered slug issub-divided, the method of manufacture preferably involves selectingthose un-machined pieces from the center and discarding thosesub-divided pieces from the end of the sintered slug. For example, wherethe sintered slug is a brick or block shaped slug, which is sub-dividedinto six un-machined pieces, the four center, and more preferably thetwo center un-machined pieces are selected for further processing whilethe end pieces are discarded. It is believed that the due to themanufacturing process involved, the center pieces will exhibit (aftermagnetization) greater magnetic (field) strength and uniformity forimproved magnetic performance.

In still further alternative embodiments, body 130 may comprise anelectro-magnet of conventional configuration that may be selectivelyenergized and de-energized so as to produce and discontinue,respectively, production of a magnetic field. The electro-magnetembodiment may be, during a blanking interval, briefly de-energized fromtime to time so as to discontinue production of a magnetic field. Theexternal magnetic field(s) used for guidance may also be discontinued insynchronism during the blanking interval. During such blanking interval,an imaging system that would otherwise experience interfering effectsdue to magnetic fields may be activated to acquire imaging data. Furtherduring such blanking interval, an external localization system may beused to acquire localization information regarding catheter 100 (orother devices) without any of the interfering effects that may otherwiseexist due to either the externally-generated magnetic fields or themagnetic field generated by the positioning magnet itself. Such externallocalization system may comprise conventional apparatus known generallyin the art, for example, an EnSite Velocity system having NAVX™ softwarefunctionality, commercially available from St. Jude Medical, Inc. and asgenerally shown with reference to commonly assigned U.S. Pat. No.7,263,397 titled “Method and Apparatus for Catheter Navigation andLocation and Mapping in the Heart,” the entire disclosure of which isincorporated herein by reference or other known technologies forlocating/navigating a catheter in space (and for visualization),including for example, the CARTO visualization and location system ofBiosense Webster, Inc., (e.g., as exemplified by U.S. Pat. No. 6,690,963entitled “System for Determining the Location and Orientation of anInvasive Medical Instrument” hereby incorporated by reference), theAURORA® system of Northern Digital Inc., a magnetic localization systemsuch as the gMPS system based on technology from MediGuide Ltd. ofHaifa, Israel and now owned by St. Jude Medical, Inc. (e.g., asexemplified by U.S. Pat. Nos. 7,386,339, 7,197,354 and 6,233,476, all ofwhich are hereby incorporated by reference) or a hybrid magneticfield-impedance based system, such as the CARTO 3 visualization andlocation system of Biosense Webster, Inc. (e.g., as exemplified by U.S.Pat. No. 7,536,218, hereby incorporated by reference). In this regard,some of the localization, navigation and/or visualization systems mayinvolve providing a sensor for producing signals indicative of catheterlocation information, and may include, for example one or moreelectrodes in the case of an impedance-based localization system such asthe EnSite™ Velocity system running NavX software, which electrodesalready exist in the case of catheter 100, or alternatively, one or morecoils (i.e., wire windings) configured to detect one or morecharacteristics of a low-strength magnetic field, for example, in thecase of a magnetic-field based localization system such as the gMPSsystem using technology from MediGuide Ltd.

FIG. 4-5 are isometric views showing a sub-assembly of tip electrodeassembly in an intermediate stage in the manufacture. In particular, tipelectrode assembly 116 includes an electrically-conductive capsule inthe form of an outer casing 146 overlying and surrounding body 130(i.e., overlying and surrounding the positioning magnet). The casing 146is configured to provide corrosion resistance for the underlying body130, which is susceptible to corrosion, in addition to providingexcellent electrical conducting characteristics. The casing 146 includesa washer (or ring) 148, a tip cap 150 and a shank cover 152.

The washer 148 includes a hole 154 and the tip cap 150 includes anopening 156. The shank cover 152, as shown, includes an opening 158, aflange 160 and a floor wall 162 having an aperture 164. In anembodiment, the components 148, 150, 152 may comprise a biocompatiblemetal, such as platinum (e.g., 99.95% Pt) or its alloys (i.e., 90%Platinum (Pt):10% Iridium (Ir)) and may have a predetermined, desiredthickness (e.g., 0.002″). In an embodiment, the metal for the componentsof casing 146 preferably has a relatively fine grain (e.g., preferablyhaving a grain size of 4 or larger, more preferably having a grain sizeof 6 or larger). Of course, variations are possible. Examples of othersuitable electrically conductive materials also include (but are notlimited to) gold, platinum, iridium, palladium, copper, nickel,stainless steel, and various mixtures, alloys and combinations thereof.In other variations, the electrically-conductive material may be appliedto the outer surface of the body 130 by known methods, such as bychemical vapor deposition (CVD), sputtering, mechanical ‘spinning’ witha mold and a tool to press sheet-form materials to the mold, plating,painting and the like.

With regard to the manufacture of the components of casing 146, washer148 may be manufactured using sheet stock of the raw material throughconventional stamping and/or cutting (e.g., laser cutting) operations.The tip cap 150 may be manufactured using a progressive, draw process,in which a blank (i.e., the raw material, which may be a 0.002″ thicksheet material in the shape of a circle in one embodiment) is fedthrough a series of dies, each progressively smaller in diameter, untilthe desired, final tip cap shape and dimension is achieved. Likewise,the shank cover 152 may be manufactured using a progressive, deep drawprocess, in which a blank is fed through a series of dies, eachprogressively smaller, until the final shape and dimension is achieved.In the case of shank cover 152, additional operations are also requiredsuch as creating flange 160 at the open end thereof and creatingaperture 164 through floor 162. As to the latter operation, a laser orstamping operation may be used. It should be understood that variationsare possible for producing the components of casing 146 (e.g.,hydroforming may be used as an alternative to a deep drawing operation).

With continued reference to FIGS. 4-5, assembly of the casing 146 tosurround body 130 involves first placing the washer 148 over the shankportion 132 through washer hole 154 and seating the washer 148 againstshoulder 142. Next, the tip cap 150 is placed on the body 130 byorienting the opening 156 of the tip cap 150 toward the distal portion134 and then inserting until the tip cap is fully seated. The shankcover 152 is likewise placed on the body 130 by orienting the opening158 toward the proximal end portion of the body shank and then insertinguntil the flange 160 is seated against the washer 148, which is itselfseated against shoulder 142.

Turning now to FIG. 6, the next step results in creating a seal at thejunction or joint 166. The proximal edge of the tip cap 150 may berolled or crimped (as shown at junction or joint 166) over the flange160 and washer 148, and then welded, for example, by laser welding. Inthis regard, the washer 148 is particularly useful where the transitionis laser welded since the washer 148 protects the underlying magnet bodyfrom the laser beam as well as provides material that is liquefied tobecome part of the weld “puddle”, thereby improving the resultant bondand seal. The casing 146 may now be considered unitary and except foraperture 164, which will be sealed as described below, providesisolation for body 130 and thus protects body 130 against corrosion.

FIG. 7 is a cross-sectional view of tip electrode assembly 116. Asshown, blind bore 144 include a floor 168. In the illustrativeembodiment, the proximal shank portion 132 of body 130 may be axiallyshorter than an inner length of the shank cover 152, thereby creating achamber 170. The extra space afforded by chamber 170 may be useful ineasing assembly of the shank cover to the shank portion of the magnetbody (i.e., reduces or eliminates dimensional interference between theproximal end of the magnet body and the inside surface of the floor ofthe shank cover).

FIGS. 8-9 are isometric views of tip electrode assembly 116,particularly the proximal end portion thereof. To provide electricalconnectivity, an electrical conductor 172 is electrically connected toconductive casing 146 at point 174 (e.g., soldered connection to theshank cover 152 on exterior of the floor wall 162). The proximal endportion of conductor 172 extends toward and terminates at electricalconnector 110. Conductor 172 may comprise conventional materials andapproaches (e.g., 34 AWG wire, insulated, solderable). As describedabove, the connector is, in turn, connected to various externalapparatus.

FIG. 9 further shows a safety line 176. The line 176 is configured torestrain and/or limit stretching of the distal assembly 112 (i.e., thesoft segment 108 of shaft 102) that may otherwise occur through repeatedadvance/retract cycles of catheter 100. The line 176 also providesadditional assurance that tip electrode assembly 116 will not disconnectfrom the catheter (i.e., from the shaft 102). In an exemplaryembodiment, a high tensile strength LCP (liquid crystal polymer) fiberwire may be used as line 176, or alternatively, line 176 may comprise ahigh strength fibrous material, for example, a para-aramid syntheticfiber commercially available under the trademark KEVLAR® from E.I. duPont de Nemours and Company, Wilmington, Del., U.S.A. One end of line176 may be affixed or anchored at connector 110 or alternatively woundaround the shaft at the proximal hub. The line 176 is also affixed atthe distal end portion specifically to tip electrode assembly 116. In anexemplary embodiment, line 176 is affixed to body 130 by tying a knot(not shown) at one end of line 176 and then press-fitting the knottedend through aperture 164 and into the blind bore 144 until seated onfloor 168. An adhesive (e.g., LOCTITE® 4981 or the like) is then appliedto bond the knot at the floor 168, as shown more particularly in FIG. 10as adhesive 178. The adhesive is then allowed to cure. The aperture 164may then be sealed by the use of a suitable adhesive/sealant, such asadhesive 178, thereby completely sealing the body 130 from potentialsources of corrosion. Adhesive 178 and adhesive 178′ may be the sameadhesive.

FIGS. 11-18 are directed to a second electrode assembly embodiment andFIG. 11 in particular is an isometric view of a single-usemagnetically-guided, open-irrigation radio-frequency (RF) ablationcatheter 200. Of course, other forms or sources of energy can beutilized in conjunction with the inventive catheters hereof, includingmicrowave, cryogenic, optical and the like. Catheter 200 includes a tipelectrode assembly 201 that includes a tip positioning magnet. A shaftof catheter 200 is shown in phantom-line and the proximal portion of thecatheter 200 (e.g., the proximal hub, etc.) has been omitted forclarity, although it should be understood that generally conventionalcatheter structures (e.g., shaft, handle, irrigation tube, etc.) may beused in connection with tip electrode assembly 201, with the exceptionthat the distal shaft section of catheter 200 may also comprise a softsegment, like soft segment 108 described above in connection withcatheter 100. Further, it should be understood that embodiments ofcatheter 200 may, and typically will, include additional structural andfunctional features that have been omitted for clarity (e.g., irrigationtube, temperature sensor and associated connecting wires, etc.).

The tip electrode assembly 201 includes a proximal passive portion 202having a first diameter that is reduced as compared to a second diameterof a distal active portion 204. The passive proximal portion is coveredby the catheter shaft and thus has no exposed, electrically-conductivesurfaces. The active distal portion remains exposed in the finalassembly (i.e., in catheter 200) and thus has an exposedelectrically-conductive surface for interaction with tissue, such as forRF ablation. As described in the Background, the magnetic material usedfor the tip positioning magnet may be susceptible to corrosion ifcontacted with irrigation fluid or body fluids. To achieve the desiredisolation from irrigation fluid, tip electrode assembly 201 includes anirrigation fluid manifold 206 into which irrigation fluid 208 (e.g.,saline solution) flows, which is destined for delivery via a pluralityof exit irrigation ports 210.

FIG. 12 is a cross-sectional view of tip electrode assembly 201. Asshown, the manifold 206 includes a distribution cavity 212 in fluidcommunication with a plurality of irrigation passageways 214. Themanifold 206 is configured to isolate the irrigation fluid from cominginto contact with the positioning magnet and can be lined or coated(e.g., with non-permeable material, insulation, or the like).

FIG. 13 is an exploded, isometric view of tip electrode assembly 201 ina preliminary stage of manufacture. The tip electrode assembly 201includes a main magnet body 216, which in turn includes an electrodebase 218 and an electrode tip 220 that together the tip positioningmagnet.

Electrode base 218 and electrode tip 220 may comprise the same magneticmaterial or electro-magnetic configuration as described above inconnection with body 130. Further, electrode base 218 and electrode tip220 may also be manufactured using the same or substantially similarmethod steps described above in connection with body 130 (i.e.,compaction, sintering, machining and magnetizing), with the exceptionthat the machining step will be somewhat different as to shape, featuresand dimensions, as described further below.

As shown, electrode base 218 is generally cylindrical and includes anaxially-extending central lumen 222 having openings on both axial endsthereof, a reduced diameter shank portion 224, an increased diameterdistal portion 226 (i.e., an increased diameter relative to the diameterof shank portion 224), a shoulder 228 at the transition between portions224 and 226 and a plurality of radially-distributed half-channels 230.The half-channels 230 have respective axes that are substantially normalto the main axis “A” of base 218.

The electrode tip 220 includes an outer distal surface 232 thatestablishes the shape for an active ablation surface, a plurality ofradially-distributed half-channels 234 that correspond to half-channels230 and an axially-arranged bore 236 that extends through electrode tip220. In one embodiment, the distal tip may be rounded (e.g., partiallyspherical or hemispherical), although other configurations may be used.

FIG. 14 is an isometric view of electrode tip 220 showingradially-distributed half-channels 234. Like the half-channels 230,half-channels 234 have axes that are substantially normal to the mainaxis “A” (when assembled).

The isolated manifold 206, in one embodiment, may comprise polyimidematerial, although it should be understood that variations in materialchoice are possible. Generally, manifold 206 comprises material thatwill isolate irrigation fluid from contact with the underlying body 216so as to inhibit or suppress the corrosive effects that irrigation fluidmay otherwise have on the magnetic material. Manifold 206 may comprisethermally nonconductive or reduced (i.e. poor) thermally conductivematerial that serves to insulate the fluid from the remaining portionsof the electrode assembly. Moreover, material(s) for manifold 206 mayalso exhibit electrically nonconductive properties. Examples of suitablematerials include, but are not limited to, polyether ether ketone(“PEEK”), high-density polyethylene, polyimides, polyaryletherketones,polyetheretherketones, polyurethane, polypropylene, orientedpolypropylene, polyethylene, crystallized polyethylene terephthalate,polyethylene terephthalate, polyester, polyetherimide, acetyl, ceramics,and various combinations thereof.

Manifold 206 includes a longitudinally-extending tubular portion 238having a cavity 212 (best shown in FIG. 12), a fluid inlet 240, and agenerally radially-distributed distal portion 242. Theradially-distributed distal portion 242 includes a plurality of tubes244 which include a corresponding plurality of irrigation passageways214 (best shown in FIG. 12). In one embodiment, manifold 206 is ofthin-wall construction (e.g., 0.002″ wall thickness) although it isrelatively rigid and thus self-supporting.

FIG. 15 is an isometric view of a first sub-assembly 246 of tipelectrode assembly 201 in a first stage of manufacture. An overallmethod of manufacture of electrode assembly 201 includes a number ofsteps. The first step involves applying a bonding material, such asepoxy, onto the outer surface of manifold 206. The epoxy may comprisebiocompatible, medical grade adhesive material(s). Second, inserting theproximal end portion of manifold 206 (i.e., opening 240 as shown in FIG.13) into the distal end portion of electrode base 218 and then slidingthe tubular portion 238 through lumen 222 until the radially-distributedtubes 244 are aligned with and are firmly seated in correspondinghalf-channels 230. The third step involves applying a bonding material,such as an electrically-conductive epoxy, on the distal, transverseouter surface of the electrode base 218 (best shown as epoxy layer 250in FIG. 17). Fourth, attaching electrode tip 220 to the electrode base218 such that (i) the axially-oriented tube 244 (i.e., extending alongthe main axis) is inserted into axial bore 236 and the exposed portionsof the remaining radially-oriented tubes 244 are aligned with and seatedin corresponding half-channels 234, thereby encasing the manifold 206within the body.

FIG. 16 is an isometric view of a further sub-assembly 248 of tipelectrode assembly 201, in a further stage of manufacture. Afterelectrode tip 220 has been attached, the next step in the method ofmanufacture involves applying an outer capsule, such as corrosioninhibiting coating 252 (best show in FIG. 17) to surround the body toisolate the body from bio-fluids to thereby inhibit or suppresscorrosion.

FIG. 17 is an exaggerated, simplified cross-sectional view of acorrosion inhibiting coating 252 for encapsulating the sub-assembly 248of FIG. 16. As described above, electrode base 218 and electrode tip 220are coupled together by a layer of epoxy 250. This is shown in FIG. 17.Coating 252 also functions to bridge the discontinuity between tip 220and base 218 due to the epoxy layer 250. Preferably, the epoxy is anelectrically-conductive epoxy, although as will become apparent, thischaracteristic is not indispensable inasmuch as the outer, exposed layerof coating 252 is also electrically conductive. Coating 252 is thusconfigured to be relatively chemically impervious to the extent ofbio-fluids, minimizing or eliminating migration of such fluids intocontact with the body. Additionally, coating 252 iselectrically-conductive, suitable for ablation, such as RF ablation. Inthe illustrated embodiment, coating 252 includes a first layer 254, asecond layer 256 and a third layer 258.

In a first embodiment of coating 252, the first layer 254 may compriseNi—Ni plating (e.g., approximately 2 mils (˜50 microns) thick), with thea first sub-layer being electroless nickel (i.e., without the use of anelectric current as typically used in electro-plating) and a secondsub-layer comprising conventional nickel plating (e.g., byelectroplating). Other conventional preparation steps, for example,surface cleaning steps (e.g., via use of an acid) and/or inter-layersurface preparation steps, may also be performed as understood by one ofordinary skill in the art. The second layer 256 may comprise gold (Au)material (e.g., approximately 2 microns thick) while the third layer 258may comprise platinum (Pt) material (e.g., approximately 1 mil (˜25microns) thick).

In a second embodiment, the first layer 254 may also comprise Ni-Niplating (e.g., approximately 2 mils (˜50 microns) thick), the secondlayer 256 may comprise titanium (Ti) material (e.g., as by dcsputtering, approximately 20,000 Å thick) while the third layer 258 maycomprise platinum (Pt) material (e.g., approximately 10,000 Å thick).

In both embodiments, the layers 254, 256 and 258 cooperate to form amulti-layer bonded surface/seal. In addition, in some embodiments, anadditional nickel (Ni) “strike” (e.g., 1 Angstrom) may be applied on topof the Ni—Ni layer 254 to reactivate the nickel. This nickel strike maybe desirable when some time has passed after the Ni—Ni layer has beenapplied before the second layer 256 is to be applied.

A further step, for example in a method for manufacturing catheter 200,involves making the necessary electrical and irrigation fluid supplyconnections between the electrode assembly and the catheter shaft andthen embedding the proximal passive portion of tip electrode assembly201 into the inside diameter portion of the shaft of catheter 200 (bestshown in FIG. 11).

FIG. 18 is an isometric view of tip electrode assembly 201 showinguntrimmed tail ends 260 of irrigation tubes 244. In an alternateembodiment for manufacturing tip electrode assembly 201, tubes 244 maybe kept longer than ultimately necessary for the final assembly (i.e.,extending beyond the surface of the electrode) so as to prevent blockageof the irrigation ports. In this alternate embodiment, the additionallength of the tubes 244 may preferably be trimmed flush with the tipsurface.

FIGS. 19-24 are directed to a third electrode assembly embodiment andFIG. 19 in particular is an isometric view of a single-usemagnetically-guided, open-irrigation RF ablation catheter 300 havingsuch an electrode assembly (i.e., tip electrode assembly 301). Thedistal portion of a shaft of catheter 300 is shown in phantom while theproximal portion of catheter 300 (e.g., the proximal hub, etc.) has beenomitted for clarity, although it should be understood that generallyconventional catheter structures (e.g., shaft, handle, irrigation tube,etc.) may be used in connection with tip electrode assembly 301, withthe exception that the distal shaft section of catheter 300 may alsocomprise a relatively flexible segment, like segment 108 described abovein connection with catheter 100. Further, it should be understood thatembodiments of catheter 300 may, and typically will, include additionalstructural and functional features that have been omitted for clarity(e.g., irrigation fluid feed tube, temperature sensor(s) and associatedconnecting wires, etc.).

The tip electrode assembly 301 includes a proximal passive portion 302having a first diameter that is reduced as compared to a second diameterof a distal active portion 304. The passive proximal portion is coveredby the catheter shaft and thus has no exposed, electrically-conductivesurfaces. The active distal portion remains exposed in the finalassembly (i.e., in catheter 300) and thus has an exposedelectrically-conductive surface for interaction with tissue, such as forRF ablation. The constituent components of tip electrode assembly 301,from radially innermost to radially outermost, include a tip positioningmagnet body 306, an isolated manifold 308 and an electrically-conductivecapsule in the form of a casing 310 that surrounds the manifold 308. Thecasing 310 includes a tip cap 312, a shank cover 314 and a washer 316(best shown in FIG. 23). Irrigation passageways 318 in electrodeassembly 301 are created between an outside surface of a plurality oflongitudinally-extending grooves 320 and the inside diameter (ID) ofcasing 310 (both the tip cap 312 and shank cover 314). The irrigationpassageways 318 lead to a plurality of exit ports. In this regard, thetip cap 312 includes a plurality of apertures 324 that include suchirrigation exit ports. The casing 310 (including constituent components312, 314 and 316) may comprise the same materials as casing 146described above for tip electrode assembly 116. Additionally, thecomponents of casing 310 may be fabricated using the same methodsdescribed above in connection with the components of casing 146.

FIG. 20 is a partial cross-sectional view of the proximal end portion oftip electrode assembly 301. The shank cover 314 includes a cylindricalouter wall 326 that extends into a base wall 328. Wall 328 includes anaperture 330. An irrigation fluid tube 332 is shown disposed in aperture330 and into which irrigation fluid 208 flows. As described in theBackground, the magnetic material used for body 306 may be susceptibleto corrosion. Accordingly, tip electrode assembly 301 also includesmanifold 308 through which irrigation fluid 208 flows destined fordelivery via ports 324. FIG. 20 better shows how the irrigationpassageways 318 are created between the outside diameter (OD) surface320 of the manifold and the inside diameter (ID) surface 322 of wall326. FIG. 20 further shows how manifold 308 isolates the irrigationfluid from contact with the positioning magnet, thereby preventing theabove-mentioned corrosion.

As further shown in FIG. 20, tip electrode assembly 301 includes adistribution cavity generally at the outlet of irrigation tube 332,which feeds fluid to irrigation passageways 318. The distribution cavityis bounded generally by base wall 328, the proximal-most portion ofsidewall 326 adjacent to base wall 328 and the proximal-most end surfaceof the coated body 306.

FIGS. 21-22 are isometric views showing a sub-assembly of tip electrodeassembly 301 in an initial stage of manufacture. A method of manufactureincludes a number of steps. The first step involves producing body 306,and in this regard body 306 may comprise the same magnetic materials orelectro-magnetic configuration as described above in connection withbody 130. Further, body 306 may be manufactured using the same orsubstantially similar method steps described above in connection withbody 130 (i.e., compaction, sintering, machining and magnetizing), withthe exception that the machining step will be somewhat different, withdifferent shapes, features and dimensions, as described further below.

The next step involves applying an isolation layer to body 306 tothereby surround the body and establish one part of the isolatedmanifold 308. The isolation layer may comprise the same material asdescribed for manifold 206, and in one embodiment, comprises a polyimidecoating. As shown, the sub-assembly 334 includes a shank portion 336, atip portion 338 and shoulder portion 340 located where the shank portion336 and the tip portion 338 meet. It should be understood that body 306is in substantially the same shape as shown in FIGS. 21-22 (whichinclude the isolation layer) and thus includes all the same features.Accordingly, as described above, body 306 may also be machined so as toinclude all such features, including axially extending grooves 320.

FIG. 23 is an isometric view of a further sub-assembly 342 in a furtherstage of manufacture. The next step in the manufacture of tip electrodeassembly 301 includes assembling the casing 310 over and onto body 306,which assembling step includes a number of sub-steps. The first sub-stepinvolves sliding washer 316 over the shank portion 336. The secondsub-step involves inserting the shank cover 314 over the shank portion336 and then advancing the distal edge thereof until washer 316 isseated against shoulder 340, with the shank cover flange seated againstwasher 316. As shown, grooves 320 include distal-most portions,designated as portions 344.

FIG. 24 is an isometric view of tip electrode assembly 301. The nextsub-step includes inserting the tip cap 312, which includes firstaligning the apertures 324 with the grooves 320. After the tip cap 312has been fully inserted, the proximal edge 346 thereof is rolled (orcrimped) and then welded (e.g., laser welded), in a manner that may bethe same as described and illustrated above (FIG. 6) in connection withcatheter 100. A further step, for example, in a method to manufacturecatheter 300, the electrical connections (e.g., for ablative energy) andirrigation supply connections are made between the electrode assemblyand the catheter shaft. Finally, the passive proximal end portion of tipelectrode assembly 301 is coupled to the distal end portion of thecatheter shaft.

FIGS. 26-30 are directed to a fourth electrode assembly embodiment andFIG. 26 in particular is a side view of a single-usemagnetically-guided, irrigated RF ablation catheter 400 having a distaltip assembly 402 that includes a multi-segment tip positioning magnetbody 404. The distal portion of a shaft 406 of catheter 400 is shown inphantom while the proximal portion of catheter 400 (e.g., the proximalhub, etc.) has been omitted for clarity, in particular for visibility ofthe outer surface of magnet body 404. It should be understood thatgenerally conventional catheter structures (e.g., shaft, handle,irrigation tube, etc.) may be used in connection with tip electrodeassembly 402, with the exception that the distal shaft section ofcatheter 400 may also comprise a relatively flexible segment, likesegment 108 described above in connection with catheter 100. Further, itshould be understood that embodiments of catheter 400 may, and typicallywill, include additional structural and functional features that havebeen omitted for clarity (e.g., irrigation fluid feed tube, temperaturesensor(s) and associated connecting wires, etc.).

FIG. 27 is an end view of magnet body 404, showing a central throughbore 408. Bore 408 is configured in size and shape to accommodate anirrigation fluid delivery tube 410 (best shown in FIG. 26) configured totransport irrigation fluid 208 from a proximal end portion 412 of magnetbody 404 to a distal end portion 414. The tube 410 is configured to matewith a corresponding inlet of a manifold portion (not shown) of anirrigated ablation tip 416, shown in block form in FIG. 26. Irrigatedtip 416 may comprise conventional configurations and materials (e.g., aPlatinum (Pt) material ablation tip having a distal ablation surface aswell as one or more irrigation ports for delivery of irrigation fluid,which may be distal exit ports, side exit ports and angled exit ports).In an embodiment, the magnet body 404 has a substantially continuousouter surface 418. Note that the magnet body 404 is isolated fromirrigation fluid 208 as well as bio-fluids, thereby preventingundesirable corrosive effects described above. It should be understoodthat a non-irrigated electrode tip may be substituted for tip 416 (i.e.,for a non-irrigated ablation catheter or non-irrigated electrodecatheter for non-ablation purposes, such as for mapping or otherdiagnostic or therapeutic purposes).

FIG. 28 is an enlarged view of FIG. 27 showing magnet body 404.Multi-segment magnet body 404 includes a plurality of axially-extending,circumferential segments. FIG. 28 shows a four segment embodiment,having segments (clockwise) 404 ₁, 404 ₂, 404 ₃ and 404 ₄ although itshould be understood that a fewer or a greater number of segments may beemployed (e.g., a two segment magnet, a six segment magnet, a thirty-sixsegment magnet, etc.). In one embodiment, each segment is individuallymagnetized to establish radially-directed magnetic orientations shown asorientations 420 ₁, 420 ₂, 420 ₃ and 420 ₄. In FIG. 28, the segments 404₁, 404 ₂, 404 ₃ and 404 ₄ are magnetized and arranged relative to eachother so that the respective North (N) poles face in a radially-inwardlydirection. Through the foregoing arrangement, the collective magneticfield lines emanating from the North poles are combined, therebyincreasing a peak magnetic field strength produced by the multi-segmentmagnet body 404 compared to a non-segmented magnet. The circumferentialextent (i.e., in degrees) of each segment is such that, when assembled,the plurality of segments extend through approximately 360 degrees. Eachsegment includes respective engagement surfaces 422 (shown for segment404 ₁ only). The multi-segment magnet body 404 includes an axial lengthand an outside diameter. In the illustrated embodiment, an aspect ratioof the axial length to the outside diameter is several times greaterthan one, although it should be understood that in alternateembodiments, an aspect ratio of one or less may be provided,particularly in view of the increased, peak magnetic field strength (B)levels achieved by a multi-segment magnet body.

FIG. 29 shows a thin-walled cylindrical retention sleeve 424 used in anembodiment for manufacturing a multi-segment magnet body 404 oralternatively an alternating pole magnet body such as magnet body 446(best shown in FIG. 32 below). The sleeve 424 includes a relativelythin-wall 426 whose inner surface 428 is coated with a lubricant (e.g.,polytetrafluoroethylene, commercially available under the tradedesignation TEFLON® from E.I. du Pont de Nemours and Company,Wilmington, Del., U.S.A.). The lubricant is selected so as to inhibitadhesion of an adhesive (more below) to the inside wall of the sleeve424 when binding the individual segments together. The sleeve 424 has aninside diameter corresponding to an outside diameter of themulti-segment magnet body 404.

With reference to FIG. 29, a method of manufacturing a multi-segmentmagnet body includes a number of steps. The first step involvesproviding a sleeve (i.e., such as sleeve 424) for retaining theplurality of individual segments during adhesive cure. The second stepinvolves producing a plurality of segments each comprising magneticmaterial and each having a circumferential extent such that theplurality of segments, collectively, extend through about 360 degrees.In this regard, a sub-step involves first producing an intermediatemagnet body. The intermediate magnet body may comprise the same magneticmaterials as described above in connection with magnet body 130 andwhich may include the same or substantially similar method stepsdescribed above in connection with magnet body 130 (i.e., compaction,sintering, machining and magnetizing), with the exception that themachining and magnetizing steps will be somewhat different, withdifferent shapes, features and dimensions, as described further below.

In particular, after a sintered slug has been machined to a desiredoutside diameter and after producing a through-bore 408 (e.g.,drilling), the individual magnet segments 404 ₁, 404 ₂, 404 ₃ and 404 ₄may be produced by longitudinally cutting the intermediate magnet body(workpiece).

The third step of the method of manufacturing includes magnetizing theplurality of segments in accordance with a predetermined magnetizationstrategy. The magnetization strategy may be to produce either auni-polar multi-segment magnet body (e.g., like magnet body 404 shown inFIG. 28) or alternately to produce an alternating pole multi-segmentmagnet body (e.g., like magnet body 446 shown and described below inconnection with FIGS. 32-35A-35B). In the case of a uni-polarmulti-segment magnet body, all of the plurality of segments aremagnetized the same way so as to establish the same radially-directedmagnetic orientation (e.g., with the N pole directed radially inwardlyand the S pole radially outwardly) in each segment. In the case of analternating pole multi-segment magnet body, however, a number ofsub-steps are performed. The sub-steps include first magnetizing half ofthe plurality of segments in a first radially directed magneticorientation and second magnetizing the remaining half of the pluralityof segments in a second radially directed magnetic orientation that isopposite that of the first magnetic orientation. In an embodiment, thefirst magnetic (radial) orientation may be where the North (N) magneticpole resides on the radially-innermost portion of the segment and theSouth (S) magnetic pole resides on the radially-outermost portion of thesegment (e.g., this magnetic orientation is shown in segment 4041 inFIG. 28), while the second magnetic orientation is opposite (i.e., Npole resides on the radially outermost portion of the segment and the Spole resides on the radially innermost portion, such as segment 4462 inFIG. 32).

The fourth step in the method of manufacturing involves applying anadhesive to the respective engagement surfaces 422 (best shown in FIG.28) of the individual segments of the multi-segment magnet body. Theadhesive may comprise suitable biocompatible medical grade adhesives,and may comprise epoxy, cyanoacrylate (CA), or other suitable adhesivescurable through any suitable mechanisms.

The fifth step involves inserting the segments, having the appliedadhesive, into the retention sleeve 424 in a predetermined arrangement.In a uni-polar (e.g., magnet body 404) magnet embodiment, thepredetermined arrangement is an arrangement wherein all the segments,including adjacent segments, have the same magnetic orientation. In analternating pole magnet embodiment (e.g., magnet body 446 in FIG. 32),the predetermined arrangement is an arrangement wherein adjacentsegments in the multi-segment magnet body have the opposite magneticorientation. In the uni-polar multi-segment magnet embodiment, thearrangement of the segments, in view of the individual magneticorientations, will produce a repulsive force tending to oppose theradially-inward assembly of the individual segments. The sleeve 424 isthus used to force the segments together, despite the repulsive,opposing force. The sleeve 424 is sized so that its inside diameter isjust slightly larger (i.e., essentially corresponds to) that the outsidediameter of multi-segment magnet, ensuring a tight fit of the individualsegments while the adhesive cures.

The sixth step involves curing the adhesive to thereby bind the segmentstogether to produce the multi-segment magnet body. Once the adhesive hascured, the completed multi-segment magnet body may be removed from thesleeve 424. The lubricant on the inside surface 428 of the sleeve 424inhibits adhesion of the adhesive to the inside surface of the sleeve,thereby facilitating removal of the completed multi-segment magnet fromthe sleeve 424.

FIG. 30 is a chart showing the improved magnetic field strength producedin accordance with a multi-segment magnet embodiment. FIG. 30illustrates the modeled magnetic field strength of a six segment magnetbody 404 a, having exemplary dimensions of 0.080″ outside diameter(OD)×0.036″ inside diameter (ID)×0.500″ axial length. As shown, thefield strength B (in gauss) is plotted as a function of a position alonga working face of the multi-segment magnet body 404 a. At positions 430,438, roughly corresponding to the twelve o'clock and six o'clockpositions, the developed field strength is about 4,900 gauss. However,as the position approaches the center bore 408, the field strengthincreases (e.g., at positions 432, 436) to a peak of about 19,000 gauss.In the center of the bore (i.e., at position 434), the field strengthdecreases again to about 4,900 gauss. The magnetic field strengthproduced by the multi-segment configuration is a number of times greaterthan conventional, unitary approaches, which may produce for similarconfigurations (e.g., as to materials, dimensions, etc.) a magneticfield strength (B) of about 4,000 gauss, for example, only.

One aspect of the improvement provided by a multi-segment magnet resultsfrom the respective, individual improvements as to the magnetization ofeach of the magnet segments. In conventional configurations, an optimummagnetizing window for magnetizing a magnet segment may be between about10-15 degrees, which is believed to be a result of the relative grainalignment in the magnet material itself.

As shown in FIG. 31, assuming a generally cylindrical magnet body isproduced so that material grain alignment is generally radially aligned,a magnet segment 440 magnetized by a single magnetizing field may haveexcellent magnetization in a central sector 442 where the material grainis aligned with such a magnetizing field but may be weaker in outersectors 444 where the grain alignment, owing to the original radialalignment, would be reduced. As a result, individual magnetization ofprogressively reduced size (as measured in degrees) segments will resultin progressively improved levels of magnetization and thus magneticfield strength production. In one embodiment, a thirty-six segmentmulti-segment magnet may be provided (i.e., 360°/10 degree sectors). Inan alternate embodiment, a twenty-four (24) segment multi-segment magnetmay be provided (i.e., 360°/15 degree sectors). Even a two-segmentmulti-segment magnet will exhibit some measure of improvement.

FIG. 32 is a simplified end view of an alternating pole multi-segmentmagnet body 446. Multi-segment magnet body 446 includes a plurality ofindividual magnet segments, which in the illustrated embodiment includesfour segments 446 ₁, 446 ₂, 446 ₃ and 446 ₄. One difference withmulti-segment magnet body 446, as compared to the multi-segment magnetsof FIGS. 26-31, is that the magnetic orientation of adjacent segments isnot the same, but rather, is opposite so as to produce an alternatingpole configuration. In other words, the radially-outermost surface ofmagnet body 446, taken clockwise, presents the following sequence ofmagnetic poles: S-N-S-N. Likewise, the radially-innermost surface ofmagnet body 446, taken clockwise, presents the following sequence ofmagnetic poles: N-S-N-S. The alternating pole configuration, while inthe presence of a suitably configured external magnetic field, may beused to develop rotation of the magnet body 446 in the rotary directionsof double-headed arrow 448 about an axis 450, which extends into thepaper in FIG. 32. It should be understood that while the exemplaryalternating pole, multi-segment magnet body 446 includes four segments,this number is exemplary only and not limiting in nature (i.e., thenumber of segments may be an even number such as two, four, six, eight,twenty-four, thirty-six, etc.). A suitably configured external magneticfield may involve communication with the external field or fieldgenerator, and in addition, may involve having to pulse theexternally-generated field to achieve rotation.

Referring to FIG. 33, in one embodiment, an alternating polemulti-segment magnet may be used in a lumen clearing device, such as adevice 452. The device 452 includes a shaft having proximal and distalend portions with a rotatable portion 454 located at the shaft distalend. The portion 454 is rotatable by virtue of inclusion of analternating pole multi-segment magnet (not shown in FIG. 33), forexample, the same or similar to magnet body 446 in FIG. 32. The device452 is shown in a body lumen 456, such as a vein or an artery of ahuman, which lumen 456 has an obstruction 458, such as plaque or thelike. An external field generator (not shown) may be configured toestablish a suitable magnetic field configured to rotate the rotatableportion 454 (i.e., via rotation of the included alternating polemulti-segment magnet) about a main axis. The rotational movement maygenerally be a reciprocating movement or alternatively a completerevolutionary movement. In the latter case, the device 452 may include aconventional swivel type joint 460 or the like to allow for completerevolutionary movement. The rotatable portion 454 may include an outerclearing structure coupled to move together with the movement of thealternating pole multi-segment magnet. The clearing structure mayconfigured in ways known in the art for effective endovascularobstruction clearing, such as by suitable surface preparation by way ofgrooves, projections, pockets or holes, surface texturing or roughening,eccentricity of shape or the like, as seen by reference to U.S.application Ser. No. 11/962,738 filed Dec. 21, 2007 (Docket No.:0E-042400US) entitled ULTRASONIC ENDOVASCULAR CLEARING DEVICE, owned bythe common assignee of the present invention, and hereby incorporated byreference in its entirety.

Referring to FIG. 34, in another embodiment, an alternating polemulti-segment magnet may be incorporated into a catheter configured foruse with a robotic catheter system, such as the robotic catheter systemin U.S. application Ser. No. 12/751,843 filed Mar. 31, 2010 entitledROBOTIC CATHETER SYSTEM (Docket No.: 0G-043516US), owned by the commonassignee of the present invention and hereby incorporated by referencein its entirety. As shown in FIG. 34, a robotic catheter system 462 isconfigured to manipulate and maneuver a catheter 464 within a lumen or acavity of a human body 466. The catheter 464 in particular may include ashaft having proximal and distal end portion as well as a rotatableportion 468 at the shaft distal end. The rotatable portion 468 isconfigured for rotation about a main axis thereof (i.e., axis A in FIGS.35A-35B) and includes (i) an alternating pole multi-segment magnet body(such as magnet body 446 in FIG. 32, not shown in FIGS. 34-35A, 35B) and(ii) a functional feature block configured to perform one of adiagnostic or therapeutic function.

For context, a robotic catheter system such as that referred to abovemay include a virtual rotation feature of the distal end portion of thecatheter, implemented using, for example, four steering wires to achieveomni-directional distal end bending without actual rotation of thecatheter shaft. In the system referred to above, the steering wires areadvanced/withdrawn using cartridges affixed to a working or control armexternal to the body. Certain diagnostic and/or therapeutic features,such as either an imaging modality or an ablation surface, however, mayhave a directionality characteristic where actual rotation of the distalend portion would be desirable so as to more properly configure thefunctional feature block for its intended use (e.g., an imagingfunctional block that needs to be rotated so that its line-of-sight isdirected to a body feature of interest or an ablation functional blockthat needs to be rotated so that an ablative energy delivery trajectoryfrom an ablative surface is directed to the tissue to be ablated, etc.).

FIGS. 35A-35B are isometric views of rotatable portion 468 in a first,initial rotary position and a second, final rotary position,respectively. In FIG. 35A, rotatable portion 468 includes a functionalfeature block 470 (e.g., an imaging modality or an ablation surface)having a directionality characteristic (e.g., line-of-sight, trajectoryof ablative energy delivery) represented by arrows 472. In FIG. 35A, theportion 468 is shown in a first, initial rotary position. However, itwould be desirable to rotate portion 468 such that the directionalityarrows 472 are directed toward body 466, which, for example, may be animaging region of interest or an ablation target tissue region.

The distal rotatable portion 468 includes an alternating polemulti-segment magnet (e.g., magnet body 446 in FIG. 32) and functionalfeature block 470, which are configured to rotate together on commonaxis A when the alternating pole multi-segment magnet is rotates. Asdescribed, the alternating pole multi-segment magnet is configured torespond to an externally applied magnetic field so as to rotate about amagnet axis thereof (which may be coincident with the common axis A). InFIG. 35A, to rotate portion 468 (and thus also the functional featureblock 470) about axis A so that the directionality arrows point to thedesired target (i.e., body 466), the rotatable portion 468 is rotated inthe direction of arrow 473 (clockwise). In an embodiment, catheter 464may further include a swivel-type joint 474 or the like configured topermit relative rotation between the portion 468 and the catheter shaft.

FIG. 35B shows portion 468 after rotation away from the first rotaryposition to the second, final rotary position. The functional featureblock 470 has likewise been rotated such that the directionality arrows(i.e., arrows 472) now point toward the intended target or region ofinterest—namely, body 466. Rotating only distal portion 468 ispreferable to rotating the entire shaft of catheter 464, or, in the caseof a robotic catheter system, rotating the entire control arm on whichthe steering wire cartridges are located. In addition, once the distalrotatable portion 468 has been rotated in a desired fashion, its rotaryposition relative to that of the catheter shaft may be selectivelylocked by lock block 476. Lock block 476 is disposed intermediate thealternating pole multi-segment magnet body 446 and the distal endportion 478 of the catheter shaft. The lock 476 may compriseconventional apparatus known in the art, suitably configured to lock therotatable portion 468 in a fixed rotary position. The lock 476 may beactuated through known electrical, mechanical (e.g., pull wire) orelectromagnetic means.

It should be further understood that the alternating pole multi-segmentmagnet may also be used in electrode catheter embodiments as describedherein (e.g., catheters 100, 200, 300 and 400, particularly catheter400). For example, the external pulsing described above used to achieverotation of the rotatable portion may be discontinued. Thereafter, theexternally-generated magnetic fields that are generated may beconfigured to interact with the local field established proximate thedistal tip in order to achieve guided movement in three-dimensionalspace.

The magnetically-guided electrode assembly and catheter embodimentsdescribed and depicted herein exhibit improved performance and in thecase of the ablation catheters, provide an irrigation function whileavoiding the corrosive effects of irrigation fluid on the tippositioning magnet. It should be further understood that while a singletip positioning magnet is depicted in the embodiments herein, thatvariations directed to multiple magnets are within the spirit and scopeof the invention.

It should be understood that ablation catheter systems may, andtypically will, include other structures and functions omitted hereinfor clarity, such as such as one or more body surface electrodes (skinpatches) (e.g., an RF dispersive indifferent electrode/patch for RFablation), an irrigation fluid source (gravity feed or pump), an RFablation generator (e.g., such as a commercially available unit soldunder the model number IBI-1500T RF Cardiac Ablation Generator,available from Irvine Biomedical, Inc) and the like, as known in theart.

It should be further understood that with respect to the irrigatedablation catheters 200, 300, variations are possible with respect to thenumber, size and placement of the irrigation passageways andcorresponding irrigation ports. For example, the invention contemplatescatheters configured to provide a plurality of cavities and/orpassageways adapted to facilitate the flow of irrigation fluidtherethrough to the manifold's outer surface (proximal irrigation) aswell as to the distal ablative surface for delivery by the distalirrigation passageways (distal irrigation). The invention furthercontemplates lateral or side discharge irrigation passageways and ports,angled (e.g., at an acute angle with respect to the main longitudinalaxis of the electrode assembly) passageways and ports as well as distalirrigation passageways and ports. The invention still furthercontemplates various further arrangements, for example, where theirrigation passageways are substantially equally distributed around thecircumference of the manifold to provide substantially equaldistribution of fluid. It should be understood that the art is repletewith various configurations and design approaches for proximal anddistal irrigation passageways and ports, and will therefore not befurther elaborated upon.

Moreover, although omitted for clarity, the shaft for each of thecatheter embodiments may include guideways (i.e., lumens) configured toallow one or more electrical connection wires to pass therethrough. Forexample, for ablation catheter embodiments, a main ablation power wirewill be connected at the proximal end portion (i.e., electricalconnector) to an RF ablation generator and routed through such aguideway and then be electrically terminated at the ablation electrodeassembly. Likewise, a temperature sensor connection wire (forembodiments having a temperature sensor, for example, thermocouples orthermistors may also follow a similar path as the power wire and then beelectrically terminated at the temperature sensor.

Although numerous embodiments of this invention have been describedabove with a certain degree of particularity, those skilled in the artcould make numerous alterations to the disclosed embodiments withoutdeparting from the spirit or scope of this invention. All directionalreferences (e.g., plus, minus, upper, lower, upward, downward, left,right, leftward, rightward, top, bottom, above, below, vertical,horizontal, clockwise, and counterclockwise) are only used foridentification purposes to aid the reader's understanding of the presentinvention, and do not create limitations, particularly as to theposition, orientation, or use of the invention. Joinder references(e.g., attached, coupled, connected, and the like) are to be construedbroadly and may include intermediate members between a connection ofelements and relative movement between elements. As such, joinderreferences do not necessarily infer that two elements are directlyconnected and in fixed relation to each other. It is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative only and not limiting.Changes in detail or structure may be made without departing from thespirit of the invention as defined in the appended claims.

1. An electrode assembly for an ablation catheter, comprising: apositioning magnet body having a proximal shank portion and a distalportion; a manifold including a distribution cavity configured toreceive irrigation fluid and an irrigation passageway coupled to saidcavity having a distal exit port for delivery of said fluid, said cavityand said passageway being isolated from said body; and an outer capsulesurrounding said body, said capsule comprising electrically conductivematerial including a distal ablation surface.
 2. The assembly of claim 1wherein said positioning magnet comprises one of a permanent magnet, apermanent magnet comprising rare earth elements and an electro-magnet.3. The assembly of claim 2 wherein said permanent magnet comprisesneodymium iron boron (NdFeB) material.
 4. The assembly of claim 1wherein said manifold includes a tubular portion having saiddistribution cavity and extending along an axis, said tubular portionincluding a proximal end portion configured to receive said fluid, saidirrigation passageway extending from a distal end portion of saidtubular portion, said passageway being in fluid communication with saidtubular portion, said manifold being disposed in corresponding recessesin said body.
 5. The assembly of claim 4 wherein said correspondingrecesses in said body include a centrally-disposed,longitudinally-extending bore configured to receive said tubular portionof said manifold.
 6. The assembly of claim 4 wherein said exit portassociated with said passageway comprises one of a distal exit port, aside exit port and an angled exit port.
 7. The assembly of claim 4wherein said irrigation passageway is a radially-extending irrigationpassageway.
 8. The assembly of claim 1 wherein said body and saidmanifold extend along an axis wherein said irrigation passageway is anaxially-extending irrigation passageway.
 9. The assembly of claim 4wherein said capsule comprises an electrically conductive coating. 10.The assembly of claim 9 wherein said coating comprises one of: (i) afirst layer of Ni—Ni material on an outer surface of said body, a secondlayer comprising gold (Au) material on said first layer and a thirdlayer comprising platinum (Pt) material on said second layer; and (ii) afirst layer of Ni—Ni material on an outer surface of said body, a secondlayer comprising titanium (Ti) material on said first layer and a thirdlayer comprising platinum (Pt) material on said second layer.
 11. Theassembly of claim 1 wherein said capsule includes (i) a cup-shaped tipcap configured to cover said distal portion of said body, and (ii) acylindrical-shaped shank cover configured to surround said shankportion, said tip cap including at least one aperture corresponding tosaid irrigation exit port.
 12. An electrode assembly for an electrodecatheter, comprising: a positioning magnet body having a proximal shankportion and a distal portion; and an outer casing surrounding said body,said casing including a cup-shaped tip cap configured to cover saiddistal portion of said body and a cylindrical-shaped shank coverconfigured to surround said shank portion of said body, said casingcomprising electrically conductive material, said shank cover beingconfigured to receive a distal end portion of a catheter shaft.
 13. Theassembly of claim 12 wherein said positioning magnet is one of apermanent magnet, a permanent magnet comprising rare earth elements andan electro-magnet.
 14. The assembly of claim 13 wherein said permanentmagnet comprises neodymium iron boron (NdFeB) material.
 15. The assemblyof claim 1 further including a safety line having distal end portioncoupled to an inner bore of said body and a proximal end.
 16. Theassembly of claim 15 wherein said safety line comprises one of liquidcrystal polymer (LCP) material and a para-aramid synthetic fiber.
 17. Amethod of manufacturing an electrode assembly for an irrigated ablationcatheter, comprising the steps of: providing a positioning magnetincluding an electrode base and an electrode tip wherein said baseincludes a proximal shank portion, an axially-extending through bore anda plurality of half-channels in a distal face; inserting a manifold insaid electrode base so that a tubular portion thereof is disposed insaid bore and so that a radially-distributed portion comprising aplurality of passageways are aligned with and seated in said pluralityof half-channels wherein said manifold isolates irrigation fluid carriedthrough said passageways from contact with said positioning magnet;affixing said electrode tip having a plurality of correspondinghalf-channels to said face of said electrode base so that saidradially-distributed portion is captured within said positioning magnet;and providing an outer capsule surrounding said positioning magnetwherein said capsule comprises electrically conductive material.
 18. Themethod of claim 17 wherein said step of providing an outer capsuleincludes the sub-step of applying an electrically conductive coating toan outer surface of the electrode base and the electrode tip.
 19. Themethod of claim 18 wherein said step of applying a coating includes thesub-steps of: applying a first layer of Ni—Ni material on an outersurface of said positioning magnet, applying a second layer comprisingone of gold (Au) material and titanium (Ti) material on said firstlayer; and applying a third layer comprising platinum (Pt) material onsaid second layer.
 20. The method of claim 17 wherein said step ofproviding an outer capsule includes the sub-steps of: placing a ringover said shank portion of said electrode base; placing an open end of acylindrical-shaped shank cover over said proximal shank; covering saidelectrode tip with a tip cap; and affixing said tip cap to said shankcover.
 21. A method of manufacturing a magnetic pellet from a workpiecethat comprises magnetizable material, said method comprising the stepsof: (A) determining a toolpath in accordance with a pelletconfiguration; (B) machining the workpiece by moving a bit along thetoolpath while rotating the workpiece; and (C) magnetizing the machinedworkpiece to thereby produce the magnetic pellet.